1. Field of the Invention
The present invention relates to an oil-impregnant sintered bearing in which a bearing main body is impregnated with lubricating oil for improving lubrication with a rotating axis member which runs through an internal diameter of the bearing, and manufacturing method thereof.
2. Related Art
An oil-impregnant sintered bearing is composed of a porous sintered metal, and is impregnated with lubricating oil prior to use. Consequently, the oil-impregnant sintered bearing can be used for a long period of time without being further oiled, has superior durability at high temperatures and low noise levels. For these reasons, it is widely used instead of a ball-bearing as a bearing for a rotating axis member.
This type of oil-impregnant sintered bearing comprises a cylindrical bearing main body of porous sintered metal, which an internal face is provided therein. A rotating axis member has a smaller diameter than the diameter of the internal face, and is inserted therein. Lubricating oil, which is sucked out from the great number of small pores which are buried in the bearing main body or opened in the surface of the internal face by the pump action accompanying the rotation of the rotating axis member, and a lubricating oil, which has been exuded by expansion caused by frictional heating, form an oil film at the section of the oil-impregnant sintered bearing which slides against the rotating axis member; this oil film supports the rotating axis member and protects it from damage such as burning.
However, in such an oil-impregnant sintered bearing, since even the sliding face, which the rotating axis member contacts while sliding, has a great number of pores which the lubricating oil is impregnated in, even when the oil film is formed between the rotating axis member and the sliding face, some of the lubricating oil leaks from the pores, reducing the oil pressure and allowing local contact between the rotating axis member and the sliding face. As a consequence, there are drawbacks that the frictional coefficient with the rotating axis member increases, and burns and the like may occur.
An oil-impregnant sintered bearing 101 shown in FIG. 4 is a conventional proposal for dealing with these drawbacks. The oil-impregnant sintered bearing 101 having an internal diameter 104, which is provide in a bearing main body 103 of porous sintered alloy having internal pores, and a rotating a is member 102, which is inserted through the internal diameter 104. A sliding face 105 is provided by closing pores in one region in the periphery direction on the inner peripheral face of the internal diameter 104. This method for preserving the oil film stops the lubricating oil from leaking when the sliding face 105 contacts the rotating axis member 102, and prevents the reduction in oil pressure mentioned above.
However, as for example disclosed in Japanese Patent Application, First Publication No. 4-307111, even when pores are closed in the inner peripheral face of a pressed powder body, obtained by pressure-forming of raw material powder, the pores sometimes re-open during sintering since tin and the like is included in the raw material powder. Consequently, oil seeps from the holes to the inside, and oil pressure decreases. Further, Japanese Patent Application, First Publication No. 5-180229 discloses technology for closing the pores in the inner peripheral face when plugging in a rod for forming the bearing at the time of post-sintering correction. However, this technology basically involves closing the pores which have appeared in the inner face, and cannot preserve the oil film since the surface layer may be broken by the oil pressure, allowing the oil to seep to the inside.
Further, Japanese Patent Application, First publication No. 8-28567 discloses technology which uses a welded material having no pores in one section of its inner peripheral face. However, since the welded material cannot contain lubricating oil, the capacity of lubricating oil which can be contained in the oil-impregnant sintered bearing is reduced.
The present invention has been realized in consideration of the above problems, and aims to provide an oil-impregnant sintered bearing which can reliably secure the oil film, formed on the sliding face, and a method for manufacturing the oil-impregnant sintered bearing.
A first aspect of the present invention provides an oil-impregnant sintered bearing comprising an internal diameter, which a rotating axis member is inserted through, provided in a bearing main body, formed by a porous sintered alloy having internal pores, and a sliding face, provided in one region of the inner peripheral face of the internal diameter. The sliding face is obtained by closing the pores which have been opened in the inner peripheral face. The density in a section preserving oil pressure, which extends from the sliding face of the bearing main body toward the outer side of the diameter, is higher than in other sections of the bearing main body.
According to this constitution, the density of the section preserving oil pressure, extending from the sliding face of the bearing main body to the outer side of the diameter, is higher than other sections of the bearing main body. Therefore, the pores in the internal area of the section preserving oil pressure are more greatly closed than the other section, with the result that oil does not seep from the sliding face to the inside, enabling the oil film to be secured over the sliding face.
A second aspect of the present invention provides a method for manufacturing the oil-impregnant sintered bearing, comprising the steps of pressure-forming a raw material powder to obtain a pressed powder body, sintering the pressed powder body, obtaining a bearing main body, formed by a porous sintered alloy having internal pores, and providing a sliding face in one region of the inner peripheral face of the internal diameter, the sliding face being provided by closing the pores which have been opened in the inner peripheral face; and making the density in a section preserving oil pressure, which extends from the sliding face of the bearing main body toward the outer side of the diameter, higher than in other sections of the bearing main body.
In this invention, the oil-impregnant sintered bearing is manufactured so that the density of the section preserving oil pressure, extending from the sliding face of the bearing main body to the outer side of the diameter, is higher than other sections of the bearing main body. Therefore, the pores in the internal area of the section preserving oil pressure are more greatly closed than the other section, with the result that oil does not seep from the sliding face to the inside, enabling the oil film to be secured over the sliding face.
According to a third aspect of the present invention, in the method of the second aspect, more raw material powder is filled in a part of a cavity for pressure-forming the pressed powder body where the section preserving oil pressure is to be provided than in other parts, and the compression rate of the raw material powder in the part during pressure-forming is made greater than in the other parts, thereby making the density in the section preserving oil pressure higher than in other sections of the bearing main body.
In this invention, in a cavity for pressure-forming a pressed powder body, more raw material powder is filled in a part where the section preserving oil pressure is to be provided than in other parts, and the compression rate of the raw material powder in the part during pressure-forming is greater than in the other parts. Therefore, when the pressed powder body is corrected after sintering to obtain the oil-impregnant sintered bearing, the density in the section preserving oil pressure can be made higher than in other sections of the bearing main body.
According to a fourth aspect of the present invention, in the method of the third aspect, the raw material powder is filled in a cavity comprised of a die for forming an outer peripheral face of the pressed powder body, which is made substantially cylindrical, a round-ended column-like core rod for forming an inner peripheral face, a first lower punch and a second lower punch for forming a bottom end face of the pressed powder body. More raw material powder is filled in a place where the section preserving oil pressure is to be provided, by bringing the first lower punch lower down than the second lower punch. In addition, the raw material powder is enclosed by the first lower punch, the second lower punch, and a upper punch, and compressed until the first lower punch and the second lower punch are set at the same height, thereby increasing the density in the place on the pressed-powder body where the section preserving oil pressure is to be provided.
In this invention, the raw material powder is filled from above into a cavity comprised of a die for forming an outer peripheral face of the pressed powder body, which is made substantially cylindrical, a round-ended column-like core rod for forming an inner peripheral face, a first lower punch and a second lower punch for forming a bottom end face of the pressed powder body. Since the first lower punch is brought lower down than the second lower punch, more raw material powder is filled in the place where the section preserving oil pressure is to be provided. The first lower punch and the second lower punch are moved upwards in the space enclosed by the die and the core rod, and the upper punch for forming the top face of the pressed powder body is inserted from above into the space enclosed by the die and the core rod and moved downwards, whereby the raw material powder is enclosed and compressed by the first lower punch, the second lower punch, and the upper punch. Since the pressed powder body is made so that the first lower punch and the second lower punch finally become the same height, the raw material powder which is filled above the first lower punch is compressed at a high compression rate. Therefore, when the pressed powder body is corrected after sintering to obtain the oil-impregnant sintered bearing, the density in the section which is filled with more raw material powder is increased, and the internal pores are more greatly closed than in other sections.
In this way, the lower punch is divided in alignment with the place where the section preserving oil pressure will be provided, the first lower punch for forming the section which will become the section preserving oil pressure being brought down lower than the second lower punch. The compression rate of the raw material powder is higher in the section which is enclosed by the first lower punch and the upper punch than in other sections. Therefore, when the pressed powder body is corrected after sintering to obtain the oil-impregnant sintered bearing, the density in the section preserving oil pressure is higher than in other sections of the bearing main body.
According to a fifth aspect of the present invention, in the method of the second aspect, the inside diameter of the inner peripheral face of the pressed powder body, which is made substantially cylindrical, is made smaller in a region where the sliding face will be provided than in other regions, and the region where the sliding face will be provided is extended toward the outer side of the diameter during correction to obtain the internal diameter, thereby compressing the section which extends to the outer side of the diameter from the region where the sliding face will be provided, and making the density of the section preserving oil pressure higher than the density in other sections of the bearing main body.
In this invention, the inside diameter of the pressed powder body in the region where the sliding face is to be provided is smaller than in other regions, and, during post-sintering correction, this section is corrected and compressed so as to expand toward the outer side of the diameter. Therefore, the density in the section preserving oil pressure can be made higher than in other sections.
A sixth aspect of this invention provides a motor equipped with a rotator having a rotating axis member which protrudes at one end, the motor comprising a worm, provided around the outer periphery of the protruding rotating axis member; and a worm wheel which meshes with the worm and has a decelerator unit provided to an output axis member protruding at a rotation core of the worm wheel. The protruding rotating axis member of the rotator is inserted into the internal diameter of the oil-impregnant sintered bearing of the first aspect, and the sliding face of the oil-impregnant sintered bearing is provided so as to slidingly contact one part of the outer peripheral face of the rotating axis member which is provided on the opposite side of the axis member line of the rotating axis member to the side which meshes with the worm wheel.
According to the constitution, the oil film, which is provided on the sliding face, is reliably preserved, guaranteeing that the rotating axis member rotates smoothly.